This invention deals with the reduction of viscosities of aqueous slurries of particulate materials and the uniform dispersion of particulate materials in aqueous systems.
It is generally known that particulate materials in aqueous slurries have a tendency to agglomerate while in the slurry and this causes the slurry to become thicker and in some cases solidify to the point where the slurry becomes a paste and is no longer pourable or pumpable. Generally, the finer the particulate materials, the greater is the tendency for them to agglomerate. Aside from the problems of high viscosity caused by such agglomeration, there are the problems of non-uniform coatings that can come about because the particulate material is not uniformly dispersed in the aqueous slurry.
Thus, it is advantageous to cause fine particulate materials to be uniformly dispersed in the aqueous slurry and one of the most common methods by which this uniform dispersion can be brought about is by simple stirring of the slurry. For those aqueous slurries that have agglomerated and whose particles are more reticent to disperse, one can use more severe means to redisperse them such as high shear mixing on suitable machinery.
More recently however it has been found advantageous to use dispersing agents to allow the particulate material to uniformly disperse in slurries and moreover, to allow the particulate material to remain dispersed, that is, non-agglomerating over long periods of time. Such materials are organic dispersants, for example, sodium polyacrylates sold as the Tamol.RTM. line of products by the Polymers, Resins and Monomers Division of Rohm and Haas Co., Philadelphia, Pa. U.S.A. These materials have limitations however, in that they are not efficient on slurries whose solids content ranges over sixty weight percent.
Other dispersants commonly used for this application are inorganic polyanionic compounds such as tetrasodium pyrophosphate but these materials decompose during storage over long periods of time.
Yet another type of dispersing agent that has been suggested are the MS-VTS copolymers (Maleic acid anhydridevinylalkoxysilane copolymers) as disclosed in U.S. Pat. No. 4,267,093, issued May 12, 1981. These materials however are limited to their use with inorganic oxidic particulate materials and, their application is explained as being useful without increasing the viscosities of the suspensions obtained. Nothing is set forth in that patent to suggest that those materials actually reduce the viscosities of high viscosity, high solids content, aqueous slurries.
Further suggested materials are those found in Russian Pat. No. 907,000, published Feb. 23, 1982, and referenced in Author's Certificate USSR No. 561721 (1975), which are sodium and potassium salts of organosilicon ethers of sulfosuccinic acid having the general formula ##STR2## wherein R is hydrogen or CH.sub.3 CO-- and M is sodium or potassium. These compounds are described as being insoluble in organic solvents which limits their usefulness as surfactants. The Russian patent specification then discloses that other new compounds, similar to those just described, which are trialkylbenzylammonium salts of bis(1,1,3,3-tetramethyl-1-propyl-3-oxypropyldisiloxane)sulfosulfoxinates having the general formula ##STR3## are also useful for lowering the viscosity of organosilicon compounds.
There is also disclosed in several patents, the use of various silanes to coat particulate materials. Such patents are for example U.S. Pat. No. 4,177,317, issued Dec. 4, 1979 and U.S. Pat. No. 4,316,807, issued Feb. 23, 1982. The former patent deals with the stabilization of chromium (IV) dioxide using silanes having the general formula R.sub.n Si(OR').sub.4-n, n-butyltrimethoxysilane and isobutyl-trimethoxysilane are preferred. The process includes the treatment of the particulate material by suspending such particulate material in an alcoholic, aqueous-alcoholic or aqueous medium containing the hydrolyzable silane and subsequently drying the particulate material to obtain particles coated with the hydrolysis product of the silane. The claim is that these treated particles do not lose their valuable magnetic properties. The latter U.S. Pat. No. 4,316,807, deals with the treatment of particulate materials using higher alkyl containing hydrolyzable silanes. This treatment is intended to increase the viscosity of the aqueous particulate system.
In U.S. Pat. No. 4,369,265, there is shown the use of an organo-silicone polymer to coat finely divided solids, such as pigments, to make them readily dispersible. An example of an organo-silicone polymer useful therein is (CH.sub.3).sub.0.67 (C.sub.6 H.sub.5).sub.1.0 Si(OC.sub.18 H.sub.37).sub.0.71 (OCH.sub.3).sub.0.04 O.sub.0.79. The inventors claim that such a treatment coats the particles and gives good dispersion properties and high volume filling.
Another U.S. Pat. No. 4,404,318 deals with pigments, dispersing agents and organic dispersing mediums wherein the dispersing agents are, for example, the reaction product of an amino resin, an alkyd resin or an acrylic resin with a silane coupling agent wherein the silane coupling agents useful therein are described as those containing amino groups such as NH.sub.2 (CH.sub.2).sub.3 Si(OC.sub.2 H.sub.5).sub.3 ; those containing a urea group such as gamma-ureidopropyltriethoxysilane; those containing a mercapto group such as HS(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3 ; those containing an epoxy group such as ##STR4## those containing haloalkyl groups such as Cl(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3 ; those containing ethylenically unsaturated double bonds such as vinyltrimethoxysilane, and mixtures thereof.
In addition, U.S. Pat. No. 4,427,824, discloses a method of dispersing fillers using hydrolyzable ester compounds such as trialkyl orthoformates, i.e., tributylorthoformate. The inventors claim that these systems are storage stable in that the pigments stay dispersed in silyl group containing compounds.
None of the prior art however deals with the additives of this invention and none of the prior art shows or makes obvious the use of such compounds in viscosity reduction and uniform dispersion of particulate material in aqueous systems.
There is a need therefore for a method of reducing the viscosities of, and causing uniform dispersibility of, particulate slurries using stable, efficient dispersing agents.